1. Field of the Invention
This invention generally relates to indicating check valves, and more particularly to indicating check valves including a switch responsive to movements of a magnet carried by a movable valve member.
2. Description of the Prior Art
While the invention has features that make it applicable for many purposes in various fields, the present disclosure is directed to detecting a slight reduction below the desired rate of fluid flowing through a piping system. For example, it may be desirable to activate a signal when a desired rate of fluid is flowing through the piping system and a warning signal when a dangerously low rate of fluid is flowing therethrough, or it may be desirable to activate or deactivate a flow indicator. Such functions generally require energizing an external electrical circuit. Of course, monitoring devices having externally located switches responsive to moving elements located within a piping system are known.
Such monitoring devices generally incorporate a magnetically responsive switch for monitoring fluids flowing therethrough such as shown, for example, in U.S. Pat. Nos. 3,549,837 and 3,549,839, each issued on Dec. 22, 1970. In these patent disclosures, a magnet is moved, by the pressure of fluid moving in the conduit, into and out of proximity with a switch externally isolated from the fluid flow and which is responsive to movement of the magnet.
However, no prior art monitoring device is known which will accurately sense or determine the rate of fluid flowing at thresholds initially activating a switch and then deactivating the switch when the rate of the flowing fluid drops slightly below the fluid flow rate initially activating the switch. While such known devices are operative to activate and deactivate the switch, they are not entirely satisfactory because they permit relatively large and indeterminate flow rates of fluid between the instances of switch activation and deactivation. It would be desirable to activate and deactivate the switch with very little difference in fluid flow rates and to be able to determine or sense the specific flow rates that activate or deactivate the switch in order to indicate a normal operating condition or an abnormal condition, respectively. One of the most serious problems confronting such a monitoring device is to control its operation so that a switch is activated at the precise instant when a desired minimum rate of fluid begins to flow through the piping system and deactivated at the precise instant when the rate of fluid flowing through the piping system begins to drop or drops below a predetermined level.